1. Technical Field
The present invention relates to a secondary battery, and more particularly, to a secondary battery module of high power and bulk size in which the connecting structure between the unit cells is improved.
2. Related Art
The non-aqueous electrolyte secondary batteries of high energy density have recently been developing as high power secondary batteries.
Several to tens of the high power secondary cells (hereinafter “unit cell”) are serially connected to form one module for motor drive of the machines requiring high power source such as hybrid electric vehicles.
The unit cell generally comprises an electrode assembly including a positive electrode, a negative electrode and a separator interposed between those two electrodes, a case having a space to receive the electrode assembly inside the case, a cap assembly fixed to the case to seal the case, and a positive terminal and a negative terminal protruding from the cap assembly to be electrically connected to the positive and negative electrodes of the electrode assembly.
To make a module, the unit cells are alternately arranged such that the positive terminal and the negative terminal of one unit cell are cross with the positive terminal and the negative terminal of the other unit cell being adjacent to the one unit cell, and the terminals are connected to each other by use of a conductive member.
While the conductive member is inserted into the terminal in order not to be separated from the terminal, it is fastened and fixed to the terminal by a nut. For this, a screw thread is formed on the outer circumference of the terminal.
As mentioned above, the conventional secondary battery module has several to tens of unit cells, which are electrically connected with the conductive member by the screw fixation method.
Since each terminal of the unit cell in the secondary battery module needs screw fixation, workload for manufacturing a module is high and large amount of time is required. Accordingly, the productivity is decreased.
In addition, when some unit cells in the secondary battery module do not work properly, it is necessary to separate the malfunctioning unit cells from the other to replace them with new unit cells or the repaired unit cells. However, this requires unscrewing the nut from the terminal and then screwing the nut to the terminal, which is inconvenient so that the manufacturing efficiency is decreased.
In addition, since the conventional conductive member has a plate shape, the contact area can not be increased when the conductive member contacts the terminal. Accordingly, it has a problem that the electrical conductivity between the terminal and the conductive member is lowered.
Especially, as the secondary battery module used for motor driven devices such as a hybrid electric vehicle requires tens of unit cells, the above problems are more serious.